1. Field of the Invention:
The present invention relates to an actuator for displacing a table through operation of a drive source to carry out mechanical work such as the conveying of a work-piece, and an actuator system which comprises a plurality of such actuators.
2. Description of the Related Art
There has heretofore been known an actuator having, as a drive source, an electric motor equipped with a sensor such as an encoder, a tachometer generator, or the like for making it possible to control a rotational speed, a drive torque, a stop position, or the like. The rotational motion from the electric motor is converted into linear motion by a drive force transmission shaft such as a ball screw, a trapezoidal screw, or the like, and the linear motion is transmitted to a table mechanism, which is displaced to convey a workpiece.
An electric motor which is incorporated in such an actuator is illustrated in longitudinal cross section in FIG. 1 of the accompanying drawings. As shown in FIG. 1, the electric motor, generally denoted at 1, has a coupling 4 interconnecting an end of a ball screw 2 and an end of a motor shaft 3 coaxially with each other. The coupling 4 serves to absorb a misalignment between the axes of the motor shaft 3 and the ball screw 2, and prevent vibrations which are produced when rotary motion is converted into linear motion and also vibrations which are produced due to rotary motion containing a flexural component perpendicular to the axis as the ball screw 2 becomes longer, from being transmitted to the motor shaft 3.
One end of the ball screw 2 is rotatably supported by a first bearing 5 comprising balls 5a which are obliquely interposed between inner and outer races thereof. Since the balls 5a bear loads at a certain angle with respect to the axis of the ball screw 2 as indicated by the broken lines in FIG. 1, the balls 5a are capable of absorbing a load in a direction substantially perpendicular to the axis of the ball screw 2 and also a load in a direction substantially parallel to the axis of the ball screw 2.
The motor shaft 3 which is housed in a motor housing 6 has an end rotatably supported by a second bearing 7 and a spring washer 8, and an opposite end rotatably supported by a third bearing 9, which is of a double bearing configuration.
The first bearing 5 supports the ball screw 2 in both axial and radially inward directions. The second bearing 7 supports the motor shaft 3 in a radially inward direction for thereby absorbing vibrations and inertial forces that are generated in a radially outward direction by the rotational forces of the motor shaft 3. The third bearing 9 supports the motor shaft 3 in both axial and radially inward directions. Therefore, in the case where a photosensor P is mounted in the electric motor 1 for detecting the number of revolutions, the rotational speed, or the like of the electric motor 1, it is possible to position an encoder disk D fixedly mounted on the motor shaft 3 accurately within a clearance A in the photosensor P.
The electric motor 1 which tends to experience a relatively high temperature during operation suffers the problem of different thermal expansions due to different materials and shapes of the parts used. Typically, the motor housing 6 is made of an aluminum-base material for heat radiation, and the motor shaft 3 is made of an iron-base material. The difference between different thermal expansions of the materials of the motor housing 6 and the motor shaft 3 causes the motor housing 6 to be displaced axially, possibly concentrating stresses on the second bearing 7 which supports the motor shaft 3. Consequently, it is necessary to absorb the difference between these different thermal expansions in some way.
In the conventional electric motor 1, the spring washer 8 is interposed between balls 7a of the second bearing 7 and an inner wall surface of a bracket 6a of the motor housing 6. The difference between the different thermal expansions can be absorbed when the spring washer 8 is elastically deformed, pressing the balls 7a in a direction substantially parallel to the axis of the motor shaft 3.
Actuators for making rotary and linear motion, such as an electric actuator represented by an electric motor and a fluid pressure actuator represented by a fluid cylinder, are controlled by a motor driver and a solenoid-operated valve. These actuators, which include actuators for use in robots, are usually disposed independently of, not integrally with, a controller.
If the electric motor 1 is incorporated as an actuator in an apparatus (not shown), thus providing a drive source, it is necessary to reduce the size and weight of the actuator as much as possible in order to increase the versatility of the actuator.
The coupling 4 which interconnects the motor shaft 3 and the ball screw 2 may bring about resonance in the motor shaft 3 and the ball screw 2 when rotated. When the electric motor 1, which requires high dynamic characteristics, as with a servomotor, resonates, the positional control accuracy thereof is lowered, and its dynamic characteristics are impaired. If the coupling 4, which-serves to prevent vibrations from being applied to the motor shaft 3, were dispensed with and the motor shaft 3 and the ball screw 2 were integrally coupled directly to each other in order to alleviate the above drawbacks, then unwanted vibrations would be transmitted to the motor shaft 3. As a result, it would be difficult to convey a workpiece continuously stably.
It is an object of the present invention to provide an actuator which allows the operator to select various actuator configurations depending on the environment in which the actuator is to be installed and the application in which the actuator is to be used.
According to a first aspect of the present invention, there is provided an actuator comprising a frame extending linearly for a predetermined length, a plurality of covers detachably and selectively mounted on respective side surfaces of the frame, a drive source, a table mechanism disposed on the frame for displacement in an axial direction of the frame in response to operation of the drive source, and drive force transmitting means for transmitting drive forces from the drive source to the table mechanism.
The covers may include a pair of side covers mounted on transverse side surfaces, respectively, of the frame, a pair of end covers mounted on longitudinal ends, respectively, of the frame, and a top cover engaging upper surfaces of the end covers. The drive force transmitting means may comprise at least a ball screw shaft or a timing belt.
The actuator may further comprise a cylinder disposed axially parallel to and outside of the frame, the cylinder having a piston rod coupled to the table mechanism.
The actuator may further comprise a cylinder disposed axially in the frame, the cylinder comprising a cylinder tube and a piston displaceable in the cylinder tube, the piston having a magnet, the table mechanism including a movable table having an inner wall surface held in sliding contact with an outer circumferential surface of the cylinder tube, the inner wall surface supporting a magnet thereon. The cylinder may comprise one or a plurality of parallel cylinders extending axially along the frame.
The actuator may further comprise a drive control block which houses at least an electric motor, a speed detecting mechanism for detecting a rotational speed of the electric motor, a brake mechanism associated with the electric motor, and a clutch mechanism associated with the electric motor. The drive control block may be composed of a plurality of blocks housing the electric motor, the speed detecting mechanism, the brake mechanism, and the clutch mechanism, respectively, the blocks being detachably coupled together.
Another object of the present invention is to provide an actuator having an electric motor including a motor shaft, a table mechanism, and a drive force transmitting shaft for transmitting drive forces from the motor to the table mechanism, the motor shaft and the drive force transmitting shaft being integrally formed with each other, thereby reducing the size and weight of the actuator.
According to a second aspect of the present invention, there is provided an actuator comprising an electric motor having a rotatable shaft, a drive force transmitting shaft for converting rotary motion from the electric motor into linear motion, and table mechanism movable by the linear motion from the drive force transmitting shaft to convey a workpiece carried on the table mechanism, the rotatable shaft and the drive force transmitting shaft being integrally formed with each other.
The electric motor may comprise a drive unit having the rotatable shaft and a detector for detecting a rotational angle of the rotatable shaft, further comprising first and second bearings, the rotatable shaft being supported at opposite ends thereof by the first and second bearings. The first bearing may be disposed near the drive unit and the second bearing may be disposed near the detector, the first and second bearings holding the rotatable shaft axially and radially thereof.
The actuator may further comprise a casing, a pair of sensors mounted in the casing, and an encoder disk interposed between the sensors and integrally coupled to the rotatable shaft, the first and second bearings maintaining a predetermined clearance between the photosensors and the encoder disk.
The electric motor may have a casing, and the actuator may further comprise a resilient member for absorbing a displacement produced due to different thermal expansions of the casing and the rotatable shaft.
The electric motor may have a casing, the rotatable shaft being removable out of the casing.
Still another object of the present invention is to provide an actuator system which can easily be reconstructed by replacing or changing actuators.
According to a third aspect of the present invention, there is provided an actuator system comprising a plurality of components including actuators, and a plurality of controllers associated with the components, respectively.
The actuators may have respective frames, the frames housing power supply buses and signal buses which interconnect the components. The signal buses may be connected to each other in a wireless configuration. The actuator system may further comprise a network communication system interconnecting the components.
The operator can freely select and mount covers of different shapes on the frame depending on the environment in which the actuator is to be installed and the application in which the actuator is to be used. Since the covers are detachable from the frame, the actuator can be modified into a different configuration by removing or adding some of the covers when the actuator is to be installed in a different place.
Vibrations produced by the drive force transmitting shaft when the motor is energized are absorbed by the first bearing, and hence prevented from being transmitted to the motor. When a displacement is generated due to the difference between thermal expansions of the casing and the rotatable shaft at the time the motor is heated, the resilient member is elastically displaced to absorb the displacement, thereby preventing stresses from being applied to the first bearing in the axial direction of the drive shaft.
The second bearing is capable of absorbing a load in the axial direction and a load in a direction perpendicular to the axial direction.
In the actuator system, each of the components of the actuator system is associated with a controller for recognizing itself. Therefore, the actuators can easily be changed.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.